Conventionally, in electrophotography, charged coloring particles (hereinafter, referred to as a toner) are brought into contact with a surface of a photoconductor or a surface of a dielectric on which an electrostatic latent image is formed, and the charged toner is made to adhere on the surface of the photoconductor or the surface of the dielectric according to an electric charge amount of the electrostatic latent image, whereby a visible image is formed. This visualization operation is generally called development.
Pulverized-type toner that is most commonly used is obtained as coloring particles with an about 5 to 10 μm average particle size by a method in which a thermoplastic resin binder for toner is thermally kneaded with pigment, charge control agent (hereinafter, also referred to as CCA), wax, and so on, and the resultant is pulverized and classified.
Further, chemical toner of suspension polymerization type which has used widely is obtained by dispersing droplets with a 5 to 10 μm average particle size in which binder resin monomers, pigment, CCA, and wax are mixed and dispersed, in water to polymerize the binder resin monomers. Further, chemical toner of an emulsion polymerization aggregation type is obtained by aggregating thermoplastic resin emulsion, wax emulsion, pigment particles, and CCA particles into from 5 to 10 μm particle size.
The most important condition for obtaining a clear developed image by using these toners is that the toner is charged with the same polarity, uniformly, and with an electric charge amount optimum for a developing system. Conventionally, in order to thus uniformly charge toner, CCA is contained in the toner, and in a case of a two-component developer, it is obtained by carrying this toner to an electrostatic latent image and mixing the toner with magnetic carrier particles for charge, or in a case of a one-component developer, it is obtained by tribocharge the toner by a charging member such as a layer regulating blade disposed on a developing roller or disposed to face the developing roller.
The frictional electric charge that the toner acquires is governed by an amount of the CCA present on a surface of the toner. Therefore, attempts have been made to make a expected amount of the CCA existing on the toner surface rather than to knead it in the toner.
For example, in JP-A 2-73371 (KOKAI) and JP-A 2-161471 (KOKAI), attempts are made to make CCA existing on a surface of a toner by using a Henschel mixer, a hybridizer, or the like.
Further, in JP-A 5-127423 (KOKAI) and JP-A 2004-220005 (KOKAI), attempts are made to fix CCA fine particles on surface of toner.
Further, JP-A 5-134457 (KOKAI) discloses a method in which CCA is precipitated from a CCA solution to a toner surface and is made finer, whereby the toner surface is covered with CCA particles.
Further, in JP-A 5-341570 (KOKAI), an attempt is made to mix a toner and an aqueous dispersion of a water-dispersible small particles with a 0.01 to 0.2 μm average particle size and CCA, and by using this dispersion, form a CCA-containing small particle layer made to fixedly adhere on a toner surface. Further, JP-A 2004-109406 (KOKAI) discloses an electrostatic image developing toner in which small particles with from 0.1 to 0.8 μm average particle size are fixed on a toner surface, with CCA being dispersed in the small particles or with the CCA adhering on surfaces of the small particles.
In general, toner is consumed when it comes into contact with a surface of an electrostatic latent image to develop the electrostatic latent image. Processes after which the toner consumed in the developing step is newly supplied, is charged again by friction with an charging member, and the development are repeated. That is, during a period when the above processes of the development and the new supply steadily continue, the toner is capable of continuous development by constantly acquiring the charge.